Low-cycle fatigue behavior of NIMONIC PE16 at room temperature
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I.
INTRODUCTION
T H E low-cycle fatigue (LCF) behavior of pure metals and alloys has been extensively studied. It'z] Detailed investigations have also been made on the fatigue behavior of some simple age-hardenable systems, like CuCo strengthened by Co precipitates t3] and A1-Cu strengthened by 0" precipitates, t4'5] Extensive studies have also been made on the fatigue behavior of nickel-base alloys containing large volume fractions of the strengthening phase T'. 16-9] The T' phase has a L12 structure and a nominal composition of Ni3(A1, Ti). However, relatively few investigations have been carried out on nickel-base alloys containing small volume fractions of y,.[~o-~5]Most of the researchers have confined their study to fatigue behavior either as a function of some particular parameters of testing or particle size. [H-151 Lerch et al. t~~ have studied the influence of y' particle size and grain size on the fatigue damage mechanisms in WASPALOY* as tested between 300 and 1073 K. In the present investigation, a nickel-base superalloy, NIMONIC** PE16, has been chosen because of its rel*WASPALOY is a trademark of Precision Rings, Inc., Indianapolis, IN. **NIMONIC is a trademark of Inco Alloys International, Inc., Huntington, WV.
atively simple microstructure consisting of a uniform distribution and a low volume fraction (maximum about 12 pct) of T' P articles.t~6] The high-temperature LCF behavior of this alloy has recently been reported by Wahi eta/. I171 The room-temperature LCF behavior, particularly the cyclic stress response, stress-strain relationship, and fatigue life, is critically examined as a function of Y' particle size [underaged (UA) to overaged (OA) state] and also of total strain amplitude. The results are discussed in the light of microstructural observations. The V. SINGH, Professor, is with the Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221 005, India. M. SUNDARARAMAN, Scientist, is with the Physical Metallurgical Division, Bhabha Atomic Research Center, Bombay 85, India. W. CHEN, Scientist, is with the Institut fiir Metallforschung, Technische Universitiit Berlin, 1000 Berlin 12, Federal Republic of Germany. R.P. WAHl, Professor, is with the HahnMeitner-Institut Berlin, 1000 Berlin 39, Federal Republic of Germany. Manuscript submitted July 5, 1989. METALLURGICALTRANSACTIONSA
cyclic stress-strain relationship has been briefly reported earlier. [i8] II.
EXPERIMENTAL
The alloy, NIMONIC PE16, used in the present investigation was supplied by M / S Glossop Superalloys Ltd., Glossop Derbyshire, United Kingdom. The chemical composition of the alloy is given is Table I. Blanks of 98-mm length and 22.4-mm diameter were solutionized at 1313 K for 1/2 hour to produce uniform, equiaxed grains of about 30/~m and subsequently aged at 1023 K for different periods of time to produce T' particles of various sizes. Measurements of diameter and number density of the T' precipitates were made on transmission electron microscopy (TEM) micrographs. To deri
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